1. Field of the Invention
The invention relates to the use of jagged cutters for the longitudinal cutting of double-face self-adhesive tapes with polypropylene (PP) backing for the purpose of edge tearability, i.e. rendering the tapes hand-tearable transversely.
The problem of edge tearability in the case of self-adhesive tapes has been present for a long time. Since adhesive tapes with plastic film backings are usually difficult to tear off by hand, use has to be made of a knife or scissors, or else the teeth if necessary.
2. Description of the Prior Art
Because of this requirement, which is so important in practice, this problem has been approached from various angles. For example, special backing films were developed, for example foamed and/or stretched, which were intended to have paper-like properties as regards their edge tearability, e.g. DE-A 3 323 018. For the high requirements in practice, however, such adhesive tapes have been found inadequate and have not been able to become established. This also includes products with a reinforcing fabric on backing film, developed especially for edge tearability, such as are described in U.S. Pat. No. 4,439,482.
It has also been proposed in the past to perforate the film backing of such an adhesive tape, e.g. U.S. Pat. No. 4,581,087, for example by means of embossing rolls, to obtain edge tearability by hand. Adhesive tapes with PP backings were also intended to have this ability by utilizing specific stretching ratios and contents of isotactic PP, e.g. DE-A 2 440 286, but this too was not able to become established in practice.
Finally, the edges of self-adhesive tapes were already worked, for example, with cutters from which parts in the cutting region had been broken out (knurled), in order thereby to effect a non-uniform cut. However, in the case of difficult-to-tear adhesive tapes with tough and resilient PP backings, in which an adhesive composition also has to be additionally cut through, such a cutting process also fails.
Therefore the object of the invention is to provide a remedy therefor, in particular to configure double-face self-adhesive tapes with PP backing to meet the high requirements of edge tearability, so that such adhesive tapes can be torn off transversely by hand without need for scissors or knives. This must not make the restrippability of the adhered tapes more difficult by, for example, undesired tearing occurring in the process.
This object is achieved according to the invention by the use of jagged cutters for the longitudinal cutting of such adhesive tapes.
Jagged cutters are known per se, being used, for example, in the production of plasters and similar medical products, to prevent fraying of fabric backings or wherever a product with a jagged edge is required for optical reasons. Such jagged cutters are therefore commercially available. Jagged cutters are also conventional, for example, integrated in unwinders, for the transverse cutting of adhesive tapes.
However, in view of the decades long existence of the problem, problem-free edge tearability in the case of double-face PP adhesive tapes, it is surprising to those skilled in the art of adhesive tape that it could be solved so easily. Even in the case of fixing products covered with release paper, the invention results in a smooth tear edge across the entire product, both in the PP backing and in the release paper, without significant force being necessary for tearing off.
It has further been found that the loss of edge adhesiveness of the rolls cut according to the invention is significantly reduced, as a result of the reduced contact area of the rolls with one another in a roll stack. By this means, the interleave discs otherwise necessary are superfluous.
The jagged cutters used preferably have jag height of approximately 0.3-6 mm, in particular 0.3-2.0 mm. preferably 0.4-1.0 mm, very particularly 0.5 mm. In this arrangement, the peak angle of a jag is preferably chosen such that the tearing force of the finished roll lies within the desired range. The more obtuse the angle, the more difficult the edge tearability becomes, reaching the value of the smoothly cut material at 180xc2x0. A peak angle of 60 to 120xc2x0, especially 90xc2x0, has proven particularly favorable. The crushing bar is 0.03 to 0.15 mm wide, preferably 0.05 mm wide.
In the case of a particularly suitable PP fixing tape covered with release paper and wound into a roll, the jagged cutter advantageously applied to the already covered fixing tape, both the adhesive tape and the release paper having the same jagged cut laterally, with easy and smooth tearability by hand.
The invention is further described in the following illustrative non-limiting example.
A jumbo roll of 1,000 m length and 1,050 mm width, mounted on a 50 xcexcm biaxially stretched PP backing, coated on both sides with 100 g/m2 of rubber self-adhesive composition and covered on one side with a silicone-treated release paper, is cut up into saleable rolls. The longitudinal cuts are made by means of crush cutters against a steel roll. The crush cutters are specially ground to obtain a jagged cut. Cutters of this kind are available from Alcon Tools, Ohio, USA. The jag height of the cutters is 0.5 mm, the peak angle of a jag is 90xc2x0. The further cutting parameters are unchanged with respect to the standard process: cutting rate 100 m/min., winding tension remains uniform without, in the process, additional machine stops occurring as a result of unintended tears.
With the use of this macroscopic jagged cutter, edge tearability is achieved even though the PP film is cut through the adhesive composition and release paper against a steel cylinder.
The carpet fixing tape thus obtained can be torn off transversely, smoothly by hand without problems and with low force.